More than 50 people are reported dead in a series of bombings in Maiduguri, capital of Nigeria's Borno state, where the Boko Haram militant group is active.

The death toll is at least 55, with around 140 people wounded, according to police.

Reports say four blasts struck the town within hours on Saturday, several of them detonated by female suicide bombers. One blast from a suicide bomber on a rickshaw hit a busy fish market. Another bomb went off at a different market, known as the Monday Market.

A VOA reporter says a group of young vigilantes have barricaded major roadways, detouring traffic and causing panic. He said several of the vigilantes stopped one of the bombers from reaching the center of the market, but lost their lives when the bomber detonated.

A state government official, Borno state Attorney General Kaka Shehu, said medical workers have been mobilized to help the victims of Saturday's violence.

On Friday, reports from Nigeria said members of Boko Haram were gathering in their stronghold of Gwoza and bringing in reinforcements from other locations.

An intelligence source who is monitoring the situation told VOA that military forces are getting closer to the town and the militants may be preparing to defend Gwoza, which is one of the last major towns they control in northeastern Nigeria.

The source says Boko Haram reinforcements are traveling to Gwoza from their refuge in the nearby Sambisa forest.

Gwoza is located about 135 kilometers south of Maiduguri.

The Associated Press reports the militants are surrounding the town with land mines and warning civilians to flee. It says the fighters have released some young women they had been holding.

VOA's source says earlier this week, militants in Gwoza killed some civilians who refused to take up arms with Boko Haram to defend the town.

In the past month, Nigeria has reported success in retaking towns and villages from Boko Haram, including the Borno state town of Mafa on Thursday.

The offensive is being aided by forces from Niger, Cameroon and Chad, all of whom have suffered Boko Haram attacks on their territory.

Earlier this week, Chad said its forces had liberated the town of Dikwa. Chad's President Idriss Deby called on Boko Haram's chief Abubakar Shekau to surrender or be killed, saying his forces know Shekau's location.

On Thursday, it was reported that Boko Haram militants killed at least 68 people in a raid on the Borno state village of Njaba. A survivor of the attack told VOA that gunmen killed all the men and teenage boys in the town, including children as young as 12 years old.

Because of the remoteness of the area, word of the attack took two days to reach the state capital, Maiduguri, about 100 kilometers away.

Boko Haram is blamed for thousands of deaths in Nigeria since launching its insurgency in 2009. The group is purportedly fighting to establish an Islamic state in northeastern Nigeria.